More than half of people between the age of 21 and 36 have their savings parked in cash, according to a new study by the Brookings Institution, reflecting extreme risk-aversion by the so-called millennial generation.

The high cash allocations to accounts like bank CDs and money-market funds, which pay little-to-no interest, suggest young adults are reluctant to put money to work in the U.S. stock market, which has bounced back from the financial crisis and recorded numerous record highs over the past year.

Citing data from UBS, the Brookings study found that 52% of millennials have their savings in cash. By comparison, all other age groups have 23% of their savings in cash. Millennials also say they only have 28% of their assets in stocks, which UBS says is “directly counter to traditional long-term investment allocation advice.”

Brookings Institution

Young adults have historically been encouraged to put money into riskier investments early in their careers in order to reap the benefits of compounding and then transition to safer investments as they get closer to retirement.

But millennials remain conservative for a number of reasons. They’ve watched their parents struggle with not one, but two severe economic recessions over the past 14 years. The stock market dropped sharply after the bursting of the tech bubble in 2000 and the housing bubble in 2008. More than five years after U.S. stocks bottomed following the financial crisis, retail investors have been slow to embrace stocks again.

Then there is the student debt issue. Young people are saddled with record levels of student debt, which makes them more conservative with whatever money they have available to save.

“One reason for this avoidance of the stock market stems from the same experience of extreme volatility and risk that the Millennials’ great grandparents experienced when they were coming of age during the Great Depression,” Brookings said in its report.